High-structure precipitated silicas

ABSTRACT

A precipitated silica having the following physico-chemical characteristics:  
                               pH (5% in water) (ISO 787-9)       3-8     BET surface area (DIN 66131)   (m 2 /g)   400-600     DBP absorption value (DIN 53601,   (g/100 g)   380-420     in relation to dried substance)     Tapped density (ISO 787-11)   (g/l)   100-200     ALPINE sieve residue &gt; 63μ (ISO 8130-1)   (%)   0.1‥40

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to precipitated silicas having ahigh structure, to a process for the manufacture of the silicas and tothe use of these silicas.

[0003] 2. Description of the Background

[0004] The structure of a silica is understood to be the extent to whichits primary particles congregate into secondary particles or,respectively, tertiary particles. The unit used to express the size ofthe structure is the Brabender dibutyl phthalate (DBP) absorptioncoefficient.

[0005] Spray dried precipitated silicas are known and sold, forinstance, under the brand name of Sipernat®. The silicas are usuallymanufactured by precipitating water glass with sulfuric acid, whereinthe entire width of possible precipitation variants can be deployed, asdescribed, for example in EP 0 078 909, U.S. Pat. No. 4,094,771 or U.S.Pat. No. 6,013,234.

[0006] After precipitation the solid matter is removed by filtration andthe filter cake is then spray-dried. If necessary, it is re-dispersed byadding an acid. Spray drying allows the manufacture of almost spherical,solid particles with a narrow size distribution range.

[0007] Silicas with DBP absorption values of up to 380 g/110 g are knownas described in EP 0 078 909. In Example 1 of the present application, asilica with 380 g/100 g DBP absorption value is obtained by spray-dryinga silica suspension containing 11% solids by weight. According toExample 5 of the present application a DBP absorption of 346 g/100 g isobtained by spray-drying a silica suspension containing 16% solid matterby weight.

[0008] A similar process is disclosed in U.S. Pat. No. 6,013,234. Inthis case a silica suspension with pH>4 and a solids content of morethan 18% by weight was spray-dried to form particles with an averageparticle diameter of more than 150 μm and a BET surface area of 100 to350 m²/g.

[0009] The known spray dried precipitated silicas can be improved withrespect to their DBP absorption values.

SUMMARY OF THE INVENTION

[0010] Accordingly, one object of the present invention is to providesilicas of improved physical characteristics.

[0011] Briefly, this object and other objects of the present inventionas hereinafter will become more readily apparent can be attained byprecipitated silicas having the following physico-chemical data: pH (5%in water) (ISO 787-9) 3-8 BET surface area (DIN 66131) (m²/g) 400-600DBP absorption value (DIN 53601, (g/100 g) 380-420 in relation to driedsubstance) Tapped density (ISO 787-11) (g/l) 100-200 ALPINE sieveresidue > 63μ (ISO 8130-1) (%) 0.1-40 

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Surprisingly, it has now been discovered that high-structuredspray-dried silicas with DBP absorption values of more than 380 g/100 gcan be obtained by employing a specific precipitation method.

[0013] Precipitated silicas of variant I of the present invention havethe following physico-chemical characteristics. Variant II III IV pH (5%in water) (ISO 787-9) 3-8 3-8 3-8 BET surface area (DIN 66131) (m²/g)400-600 400-600 400-600 DBP absorption value (DIN 53601, 380-420 380-420380-420 in relation to dried substance) (g/100 g) Tapped density (ISO787-11) (g/l) 140-200 120-180 100-130 ALPINE sieve residue > 63μ 10-40 1-10 0.1-1   (ISO 8130-1) (%)

[0014] Another variant of the precipitated silicas of the presentinvention have the following physico-chemical characteristics: Variant III III IV pH (5% in water) 3-8 3-8 3-8 3-8 (ISO 787-9) BET surface area400-600 400-600 400-600 400-600 (DIN 66131) (m²/g) DBP absorption value380-420 380-420 380-420 380-420 (DIN 53601, in relation to driedsubstance) (g/100 g) Tapped density 100-200 140-200 120-180 100-130 (ISO787-11) (g/l) ALPINE sieve residue > 0.1-40  10-40  1-10 0.1-1   63μ(ISO 8130-1) (%)

[0015] The variants of silica of the present invention can be preparedby a process in which, while stirring water in a vessel with a forcesufficient to subject the medium to shear while the water is heated to35° C. to 45° C., water and sulfuric acid are added together to themedium within at least 100 minutes. The pH is maintained at 6-7. Theintroduction of substances into the vessel is then interrupted for60-120 minutes and when the addition of the substances has beencompleted, the medium contains a solids content of 36-42 g/l. The solidsare removed by filtration, the filter cake is washed and the solidmaterial is subjected to a short retention drying process

[0016] A special variant of the process is such that while stirring avessel containing water heated to 35° C. to 45° C., preferably 36° C. to40° C. and maintaining a pH of 6-7 and adding waterglass and sulfuricacid together, while the mixture is subjected to shear during the entireprecipitation time with a disk agitator installed in addition to theagitator, by interrupting the precipitation for 90 minutes from the13^(th) to the 103^(rd) minute, after a total precipitation time of 137minutes, a final silica concentration of 38 to 42 g/l is established inthe precipitation suspension. The precipitation suspension is thenfiltered and washed, the filter cake is dried or liquefied by addingwater and/or acid to form a suspension containing 8% to 16% solidmatter. The suspension is then spray-dried.

[0017] The short retention time drying in process stage c) can beconducted by liquefying the filter cake to a solids content of less than18% by weight and spray-drying the suspension.

[0018] In another variant of the process of the present invention theshort retention time drying process can be conducted by means of aspin-flash drying process on the washed filter cake from process stageb).

[0019] The pH of the end product is of decisive importance for manyapplications of the silicas. For instance, if the silica is used as acarrier material for vitamins, a neutral or weak acidic pH is required.The pH can be modified by subsequently treating the spray-dried silicawith a base such as ammonia gas or by adjusting the pH of there-suspended filter cake.

[0020] Determination of the pH of the silica is conducted on a 5%suspension of spray-dried silica according to the procedure of ISO787-9.

[0021] The process of the present invention can be conducted under thecondition that either the pH of the precipitation suspension is notmodified after precipitation or the pH is lowered to 2-5, preferably 3,by adding acid, e.g. sulfuric acid.

[0022] The solid matter is separated from the suspension by knownfiltration methods such as a filter press (diaphragm filter press). Thefilter cake obtained in this way can be dried, for example by using aspin flash dryer. It is also possible to liquefy the filter cake byadding water and/or acid. If acid is employed, e.g. diluted sulfuricacid, a pH of <5, preferably 2-4, is adjusted in the suspension.

[0023] In a special embodiment of the process of the present invention,the product that has been subjected to a short retention drying processis subsequently treated with ammonia gas, or, alternatively, the dryingprocess is conducted in the presence of ammonia gas.

[0024] Adding ammonia gas increases the pH of the silica and enableshigher DBP absorption values.

[0025] A specified particle size distribution can be adjusted with theaid of a spray dryer or a jet dryer (jet tower). This can be adjusted byselecting the dryer type (single material jet, 2 material jet,gas/liquid jet, atomizing disk) and the spraying pressure. Typically adryer with an atomizing disk is used.

[0026] Silicas of the present invention can be used as a carrier forconverting liquids into powder form, e.g. in the crop protection,pesticide and animal feed industries, e.g. vitamin A and E, cholinechloride, as a free-flow or anti-caking agent, for example for tablesalt or instant meals, as well as in elastomers such as tires.

[0027] The silicas according to the present invention can be used tomanufacture catalyst carriers.

[0028] Having now generally described this invention, a furtherunderstanding can be obtained by reference to certain specific exampleswhich are provided herein for purposes of illustration only and are notintended to be limiting unless otherwise specified.

EXAMPLES Reference Example 1

[0029] Precipitation of silica material is conducted as described inExample 1 of EP 0 078 909. For this purpose 60 m³ of water at atemperature of 40° C. was added to a precipitation vessel, fitted withan EKATO MIG agitator and an additional EKATO shearing turbine.Commercially available water glass (26.8% SiO₂; 8.0% Na₂O; density1.346) and sulfuric acid (96%) flow into this vessel simultaneously at aspeed of 10 m³/h and 0.9 m³/h respectively. After the 13^(th) minute ofprecipitation the addition of water glass and acid is interrupted for 90minutes. During this time both stirring devices continue to operate.From the 103^(rd) minute the water glass and acid are added once more,at the above-mentioned rates, until the 146^(th) minute. The solidscontent of the precipitation suspension is 47 g/l.

[0030] The solid of the suspension is removed by filtration in filterpresses, washed and the resulting filter cake is liquefied under theeffects of shearing. The solids content is 11.0%, the pH is 5. Thesilica suspension is then spray-dried. A DBP absorption value of 355g/110 g was determined for the product that was obtained in the abovemanner.

[0031] The characteristics of the non-comminuted product are shown inthe table below.

Reference Example 2

[0032] A precipitated silica was manufactured by the procedure describedin Example 5 of EP 0 078 909. The procedure only differs from that ofReference Example 1 in the manufacture of the silica suspension forspray-drying. The filter cake is adjusted to a solids content of 16% byweight and a pH of 4.5 by adding water and acid under shearingconditions. The DBP absorption value is 349 g/100 g.

[0033] The characteristics of the non-comminuted product are found inthe table below.

Example 1

[0034] An amount of 60 m³ of water at a temperature of 38° C. was addedto a precipitation vessel, fitted with an EKATO MIG agitator and anadditional EKATO disk agitator (350 mm diameter). While maintaining a pHof 6.5, commercially available water glass (27.1% SiO₂; 8.07% Na₂O;density 1.355) and sulfuric acid (96%) flow into this vesselsimultaneously at a speed of 10 m³/h and 0.9 m³/h respectively. The acidis made to flow over the disk agitator, which is started whenprecipitation begins. After 13 minutes precipitation time, the additionof water glass and acid is interrupted for 90 minutes. During this timeboth the agitator and the EKATO disk agitator continue to operate. Afterthis time the water glass and acid are added once more, at theabove-mentioned rates and maintaining the above-mentioned pH for afurther 34 minutes. The suspension is then acidified to pH 3 by addingsulfuric acid. The solids content of the precipitation suspension is 40g/l. The suspension is subsequently filtered and washed in filterpresses. For the further processing stage the filter cake is liquefiedunder shear with the addition of water and small quantities of sulfuricacid. The pH is 5.0; the solids content is 12%. The silica suspension isthen spray-dried. The free sulfuric acid in the material is neutralizeddownstream of the spray dryer with ammonia gas.

[0035] The characteristics of the non-comminuted product are found inthe table below.

Example 2

[0036] A precipitated silica is manufactured as described above inExample 1, except that the filter cake obtained after processing in thediaphragm filter press is liquefied under shear with the addition ofwater and small quantities of sulfuric acid. The pH is 5.0 and thesolids content is 11.0%. The silica suspension is then spray-dried.

Example 3

[0037] The precipitated silica is manufactured by the procedure ofExample 1 above, except that the filter cake obtained after processingin the diaphragm filter press is liquefied upon the addition of water.The solids content is 8%.

[0038] The characteristics of the non-comminuted product are describedin the table below.

Example 4

[0039] The precipitated silica is manufactured according to theprocedure of Example 1 above, except that the filter cake obtained afterprocessing in diaphragm filter presses with a solids content of 18% isdried for further processing in a spin flash dryer. (O. T. Kragh,Keramische Zeitschrift, Vol. 30, issue 7, pp 369-370, 1978; T.Hoepffner, Informations Chemie, Vol. 342, pp 141-145, 1992).

[0040] The characteristics of the non-comminuted product are shown inthe table below.

Example 5

[0041] The precipitated silica is manufactured according to theprocedure of Example 1 described above, except that the precipitationsuspension is not acidified after precipitation is complete. Thesuspension is filtered in diaphragm filter presses and washed withhighly diluted sulfuric acid with a pH of 1.6 to 1.8. For furtherprocessing the filter cake with a solids content of 18% is dried in aspin flash dryer. The free sulfuric acid contained in the material fromthe washing process is neutralized by adding ammonia, or, alternatively,the pH in the powder is raised to 7.7.

[0042] The characteristics of the non-comminuted product are shown inthe table below.

Example 6

[0043] Manufacture of a precipitated silica and the subsequentprocessing of the suspension, including washing were conducted accordingto the procedure described in Example 4 above, except that for furtherprocessing the filter cake is liquefied by adding water under shearconditions. The pH is 3.2; the solids content is 11%. To neutralize thefree sulfuric acid, the material is neutralized with ammonia gasdownstream of the spray-dryer.

[0044] The characteristics of the non-comminuted product are shown inthe table below. TABLE Reference Examples Examples 1 2 1 2 3 4 5 6 pH6.4 6.2 7.6 6.7 6.7 6.4 3.1 4.7 6.3 7.0 7.7 6.3 DBP absorption g/100 g355 349 389 382 400 387 383 391 398 406 412 387 value Tapped density g/l180 182 154 154 135 120 119 115 111 108 111 164 ALPINE SR > % 10 23 151.4 1.8 0.3 0.2 0.3 0.3 0.2 0.1 18 63 μm BET surface m²/g 429 515 454458 485 484 501 476 495 area Suspension pH ˜6 ˜3 ˜7 Washing normalnormal acidic process Suspension of pH 5 4.5 5 5 5 N/A N/A (Filter cakehas pH˜3) 3.2 filter cake Solids % 11 16 12 11 8 18 18 11 content NH₃addition — — + — — — — + + + + + + Dryer SP SP SP SP SP SF SF SF SF SFSF SF SP

[0045] The disclosure of German priority Application No. 10058616.3dated Nov. 25, 2000 is hereby incorporated by reference into the presentapplication.

[0046] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is,therefore, to be understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed herein.

What is claimed as new and is intended to be secured by Letters Patentis:
 1. A precipitated silica having the following physico-chemicalcharacteristics: pH (5% in water) (ISO 787-9) 3-8 BET surface area (DIN66131) (m²/g) 400-600 DBP absorption value (DIN 53601, (g/100 g) 380-420in relation to dried substance) Tapped density (ISO 787-11) (g/l)100-200 ALPINE sieve residue > 63μ (ISO 8130-1) (%) 0.1-40 


2. The precipitated silica according to claim 1, which has the followingphysico-chemical characteristics: pH (5% in water) (ISO 787-9) 3-8 BETsurface area (DIN 66131) (m²/g) 400-600 DBP absorption value (DIN 53601,(g/100 g) 380-420 in relation to dried substance) Tapped density (ISO787-11) (g/l) 140-200 ALPINE sieve residue > 63μ (ISO 8130-1) (%) 10-40 


3. The precipitated silica according to claim 1, which has the followingphysico-chemical characteristics: pH (5% in water) (ISO 787-9) 3-8 BETsurface area (DIN 66131) (m²/g) 400-600 DBP absorption value (DIN 53601,(g/100 g) 380-420 in relation to dried substance) Tapped density (ISO787-11) (g/l) 140-180 ALPINE sieve residue > 63μ (ISO 8130-1) (%)  1-10


4. The precipitated silica according to claim 1, which has the followingphysico-chemical characteristics: pH (5% in water) (ISO 787-9) 3-8 BETsurface area (DIN 66131) (m²/g) 400-600 DBP absorption value (DIN 53601,(g/100 g) 380-420 in relation to dried substance) Tapped density (ISO787-11) (g/l) 100-130 ALPINE sieve residue > 63μ (ISO 8130-1) (%)0.1-1  


5. A process for manufacturing a precipitated silica according to claim1, which comprises: while stirring water in a vessel with a forcesufficient to subject the medium to shear containing water heated to 35°C. to 45° C., a) adding water and sulfuric acid together within at least100 minutes, to the vessel and maintaining a pH of 6-7, wherein theaddition of substances is interrupted for 60 to 120 minutes and when theaddition of the substances to the vessel has been completed, a solidscontent of 36 to 42 g/l remains; and b) filtering the solid matter,washing the filter cake and subjecting the solid material to a shortretention drying process.
 6. The process according to claim 5, whichfurther comprises conducting a short retention time drying process (c)by liquefying the filter cake to a solids content of less than 18% byweight and spray-drying the resulting suspension.
 7. The processaccording to claim 6, wherein the short retention time drying process in(c) is conducted by drying the filter cake with a spin flash dryer. 8.The process according to claim 6, wherein the silica obtained after theshort retention drying process is adjusted to pH 7 to 8 with ammoniagas.
 9. The process according to claim 6, wherein the filter cake iswashed with diluted sulfuric acid.
 10. A method of formulating an animalfeed, comprising: combining the nutritive feed components of the feedwith the precipitated silica of claim 1 as a carrier.
 11. A method offormulating a vitamin formulation, comprising: combining the vitamincomponents of vitamin composition with the precipitated silica of claim1 as a carrier.
 12. A method of formulating a catalyst, comprising:combining the components of a catalyst with the precipitated silica ofclaim 1 as a carrier for the catalytically active components of thecatalyst.
 13. A free-flowing composition, comprising: formulating theingredients of a composition with the precipitated silica of claim 1which functions as a free-flow or anti-caking agent.
 14. A method ofconverting a liquid into powder form, comprising: combining said liquidwith the precipitated silica of claim 1 as an auxiliary therebyconverting the liquid into powder.
 15. The powder prepared by the methodof claim
 14. 16. An elastomer containing mixture prepared by combiningan elastomer with the precipitated silica of claim
 1. 17. A method ofmanufacturing a catalyst carrier, comprising: combining the componentsof a catalyst carrier with the precipitated silica according to claim 1.